Containers holding liquids and bulk solids are economically manufactured in a continuous blow molding process, wherein a parison comprising a hollow tube of molten polymer resin is extruded continuously from a flow head. The parison is acted on by a series of moving molds, each of which is formed of mold halves which are moved sequentially to a position beneath the flow head in an open configuration. The flow head is positioned above the path of the molds and is moved downwardly toward each open mold as it arrives beneath the flow head to position a portion of the parison between the mold halves. The mold halves close about the parison portion from opposite sides. As the mold halves comprising a particular mold close about, the parison portion, knives sever the parison portion from the continuously extruding parison, and a clamp pinches the end of the extruding parison to seal it, allowing the parison to be inflated to prevent it from collapsing in on itself.
The flow head is moved upwardly away from the mold path and the mold, now clear of the extruding parison, moves away from the flow head to allow the next mold to be positioned beneath the flow head and engage its respective parison portion being extruded. After a parison portion is engaged by a mold and cut from the parison, air is injected into the parison portion forcing it to expand and assume the shape of the mold. The newly molded container is allowed to cool and the mold is then opened to release the container to a conveyor, which transports the container for further processing. The mold then travels back to the flow head to mold another container.
Although such machines allow for high production rates of uniform containers, there are disadvantages in the various mechanisms and the method which, if eliminated, will result in more reliable production of high quality containers. One such problem involves the moving flow head. The parison acts as a pendulum as it dangles beneath the flow head while it is being extruded. The knives which sever the parison portion from the parison and the clamp which pinches and seals the parison cause the parison to swing when they disengage from it. Motion of the flow head tends to amplify the swinging motion of the parison, which can lead to irregularities is and flaws in the containers as the mold halves close on a parison portion that is in a different position and orientation from one mold to the next.
Mold closing also affects the quality of the molded container. It is important that the molds close in precise alignment consistently and maintain the precise alignment throughout the molding process. The molds must withstand significant internal pressure without shifting or parting to ensure a quality container with the requisite uniformity of production.
Mold cooling also affects the container production. The longer the cooling time, the less likely a container will be damaged during handling upon removal from a mold. Increased cooling time must be weighed against a decrease in output, however, and it would be advantageous if longer cooling time could be realized without adversely affecting the machine output. It would also be advantageous to provide a handling mechanism for removing containers from molds which is gentle and will not damage the container when it is most vulnerable during cooling.